Epistemology (i/ɨˌpɪstɨˈmɒlədʒi/ from Greek ἐπιστήμη - epistēmē, meaning "knowledge, understanding", and λόγος - logos, meaning "study of") is the branch of philosophy concerned with the nature and scope of knowledge and is also referred to as "theory of knowledge". It questions what knowledge is and how it can be acquired, and the extent to which any given subject or entity can be known.

Much of the debate in this field has focused on analyzing the nature of knowledge and how it relates to connected notions such as truth, belief, and justification.

The term "epistemology" was introduced by the Scottish philosopher James Frederick Ferrier (1808–1864).